The cost of fabrication remains a major consideration in connection with heat transfer panels and particularly solar energy collectors. Generally, as the efficiency of heat transfer increases, so does the cost of the panel.
In my U.S. Pat. No. 4,205,658, a heat transfer panel is set forth in which a flexible membrane is distended over a corrugated support surface and means, such as cylindrical transparent tubing, are used to distort the membrane down into the recesses in the corrugated support surface for flow of the heat transfer fluid, not only in the recessed areas, but very importantly, over the protruding areas of the corrugations. The resultant heat transfer channels are relatively thin in cross-section, and the heat transfer efficiency is relatively good, particularly when considering the low-cost construction of the panel.
Although representing a significant reduction in cost over prior panels of equal efficiency, the heat transfer panel of my U.S. Pat. No. 4,205,658 could also benefit from further reductions in cost. Thus, the manner in which the flexible membrane or envelope is retained against the corrugated support surface could be simplified with attendant cost savings.
Most unglazed solar collectors or heat transfer panels that are relatively low in cost are not self-supporting. Thus, structures such as are shown in U.S. Pat. No. 3,991,742 must be roof-mounted or placed in a special framework or support structure providing support under virtually the entire surface area of the panel. The solar collector which has been most successfully commercially developed is a relatively low-cost collector by Fafco Solar of Menlo Park, Calif. The Fafco collector, however, is formed by a plurality of side-by-side polyolefin tubing that is quite flexible, particularly when exposed to the sun. Accordingly, the Fafco collector requires a complete support surface for its installation and use.
Another aspect of prior heat transfer panels or solar collectors which has been largely disregarded is the construction of inlet and collection manifolds. Most solar panels are understandably concerned with considerations other than the distribution and collection of heat transfer fluid from the panel. Accordingly, the most common approach is just simply to employ a transverse pipe with a plurality of openings along the length thereof as the inlet manifold and a similar pipe or chamber at the opposite end of the panel as a collector. Such pipes are usually inserted into and sealed in a bag or envelope or they are built into the end of a box or containment structure for the panel. The manifolds are seldom truly integrated with the panel construction in a way which would affect panel strength or the cost of production.
Solar energy collector panels are widely marketed for home use with little or no consideration being given to the problem of safety of the user, particularly with regard to the possibility of scalding as a result of stagnation of water in the panel. The problem of scalding can occur most readily in connection with solar collectors which have glazing above the heat transfer flow channels. The glazing provides a dead air space which will permit and result in much higher temperature operation of the panel. Thus, when the solar irradiation is high, the panel flow rate may be too slow with the result that water temperature in the panel is undesirably high and can even scald the user of a home water system. An inexpensive and reliable means for dissipating heat from a glazed heat transfer panel or solar collector would be highly advantageous.